```
class Solution(object):
def summaryRanges(self, nums):
"""
:type nums: List[int]
:rtype: List[str]
"""
i, j = 0, 0
ans = []
while i < len(nums) and j < len(nums):
k = 0
while j < len(nums) and nums[i] + k == nums[j]:
j += 1
k += 1
if i+1 == j:
ans.append(str(nums[i]))
else:
ans.append(str(nums[i])+'->'+str(nums[j-1]))
i = j
return ans
```